Several centrally acting biogenic amines have been shown to bind specifically and with high affinity to lymphocyte receptors, followed by alteration of lymphocyte function. We are developing fluorescent amine derivatives with which to study these receptors in vivo using a fluorescence-activated cell sorter (FACS). We will characterize the presence of these receptors on lymphocyte subsets defined by monoclonal antibodies and determine whether their presence on these subsets has any functional significance. Long term studies to measure these receptors in transformed lymphocytes will also be undertaken.